HONG KONG (REUTERS) - Thousands of pro-democracy protesters thronged the rain-soaked streets of Hong Kong early on Wednesday, ratcheting up pressure on the pro-Beijing government that has called the action illegal and vowed to press ahead with National Day celebrations.

On the sixth day of a determined mass campaign to occupy sections of the city and express fury at a Chinese decision to limit voters' choices in a 2017 leadership election, there was little sign of momentum flagging. That was despite widespread fears that police may use force to move crowds who have brought large sections of the Asian financial hub to a standstill and affected businesses from banks to jewellers.

Thunder, lightning and heavy rain failed to dampen spirits as protesters sought shelter under covered walkways, while police in raincoats and hats looked on passively nearby. At the weekend, riot police had used tear gas, pepper spray and baton charges to try to quell the unrest, but since then tensions have eased as both sides appeared prepared to wait it out, at least for now.

Protests spread to Tsim Sha Tsui, one of the city's most popular shopping areas for mainland Chinese that would normally do roaring trade during the annual holiday marking the Communist Party's foundation of the People's Republic of China in 1949. But in the early morning hours, hundreds of demonstrators were milling around outside luxury stores and setting up makeshift barricades in anticipation of possible clashes.

As in most parts of Hong Kong, the police presence was small.

M. Lau, a 56-year-old retiree, said he had taken to the streets of Hong Kong to protest in the 1980s, and wanted to do so again in a show of solidarity with a movement that has been led by students as well as more established activists.

"Later this morning I will come back," he said. "I want to see more. Our parents and grandparents came to Hong Kong for freedom and the rule of law. This (protest) is to maintain our 160-year-old legal system for the next generation."

China rules Hong Kong under a "one country, two systems"formula that accords the former British colony a degree of autonomy and freedoms not enjoyed in mainland China, with universal suffrage set as an eventual goal. But when Beijing ruled a month ago that it would vet candidates wishing to run for Hong Kong's leadership, protesters reacted angrily and called for Hong Kong chief executive Leung Chun-ying to step down.

Student leaders had given Leung an ultimatum to come out and address the crowds before midnight on Tuesday, threatening to occupy more government facilities, buildings and public roads if he failed to do so. Leung did not comply, but has said that Beijing would not back down in the face of protests. He also said Hong Kong police would be able to maintain security without help from People's Liberation Army (PLA) troops from the mainland.

Communist Party leaders in Beijing worry that calls for democracy could spread to the mainland, and have been aggressively censoring news and social media comments about the Hong Kong demonstrations.

Mainland Chinese visiting Hong Kong had differing views on the demonstrations, being staged under the "Occupy" banner.

"For the first time in my life I feel close to politics,"said a Chinese tourist from Beijing who gave only her surname, Yu. "This is a historic moment for Hong Kong. I believe something like this will happen in China one day," added the 29-year-old.

But a woman surnamed Lin, from the southern Chinese city of Shenzhen, said the protesters' demands for a democratic election were "disrespectful to the mainland".

"Even though the government has brought a lot of development to Hong Kong, they don't acknowledge this," Lin said.

The protests are the worst in Hong Kong since China resumed its rule in 1997. They also represent one of the biggest political challenges for Beijing since it violently crushed pro-democracy protests in Tiananmen Square in 1989. Cracking down too hard could shake confidence in market-driven Hong Kong, which has a separate legal system from the rest of China. Not reacting firmly enough, however, could embolden dissidents on the mainland.

The deputy director of China's National People's Congress Internal and Judicial Affairs Committee, Li Shenming, wrote in the People's Daily: "In today's China, engaging in an election system of one-man-one-vote is bound to quickly lead to turmoil, unrest and even a situation of civil war."

Underlining nervousness among some activists that provocation on National Day could spark violence, students from Hong Kong University made an online appeal for people not to disturb the flag-raising ceremony.

"However much you dislike a country, disturbing her flag-raising ceremony is total disrespect and goes against the nature of democracy," it said, reminding readers that the international media was watching.

The outside world has looked on warily. In Britain's strongest interjection yet, finance chief George Osborne urged China to seek peace and said the former colony's prosperity depended on freedom. Washington urged Hong Kong authorities "to exercise restraint and for protesters to express their views peacefully".

The events have also been followed closely in Taiwan, which has full democracy but is considered by Beijing as a renegade province that must one day be reunited with the mainland.

On the financial markets, Hong Kong shares fell to a three-month low on Tuesday, registering their biggest monthly fall since May 2012. Markets are closed on Wednesday and Thursday for the holidays. The city's benchmark index has plunged 7.3 per cent this month, and there were few indications that the protests are likely to end any time soon.

Over the last 24 hours, people have set up supply stations with water bottles, fruit, crackers, disposable raincoats, towels, goggles, face masks and tents, indicating they were in for the long haul.

"Even though I may get arrested, I will stay until the last minute," said 16-year-old John Choi. "We are fighting for our future."

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